1. Field of the Invention
The present invention relates to a disc tray of an optical disc drive, and more particularly, to a disc tray to decrease vibration and noise generated when an optical disc rotates.
2. Description of the Related Art
In general, optical disc drives record information on a recording surface formed of a concentric circular track on an optical disc, or read information from the recording surface. More specifically, the optical disc drives record or read data by irradiating a laser beam on the recording surface of the optical disc, which rotates by a constant linear velocity method, from an optical pickup which slides in a radial direction of the optical disc.
Generally provided in the optical disc drive is a disc tray on which the optical disc is to be loaded. A window is bored through the disc tray so that the optical pickup to record or read data may access the rotating optical disc.
In order to precisely read data recorded on the recording surface of the optical disc from the optical disc drive, or to precisely record data on the optical disc, a laser beam emitted from the optical pickup should be precisely incident on a track of the recording surface of the optical disc, and an optical axis of the beam irradiated from an actuator and the recording surface of the optical disc should always be maintained at a constant angle.
However, noise and vibration, which are generated by friction between the optical disc that rotates at a high velocity and air, resistance of air, and high velocity turbulent air flow, deteriorate recording and reproduction characteristics of the optical disc drive.
Korean Patent Application Nos. 1998-0013873 and 1998-0030740 address the above problem. FIG. 1A of Korean Patent Application Nos. 1998-0013873 shows a conventional apparatus to decrease noise in an optical disc drive, and FIG. 1B shows how a velocity gradient is removed by the structure of FIG. 1A.
As shown in FIGS. 1A and 1B, a plurality of blades 110 are provided on a seating surface 101 of a disc tray 100 so that a velocity gradient of air is removed from an inside of a boundary layer formed under an optical disc 190, when the optical disc 190 is seated on a turntable (not shown) and rotates at high velocity while floating on the seating surface 101.
The plurality of blades 110 are formed on the seating surface 101 of the disc tray 100 so that each blade of the plurality of blades 110 is inclined upward at an angle of 45? in a rotation direction 180 of the optical disc 190, as shown in FIG. 1B. The plurality of blades 110 extend in a radial direction of the optical disc 190, as shown in FIG. 1A.
When the optical disc 190 rotates at high velocity, a velocity gradient 150 which gradually increases toward the seating surface 101 of the disc tray 100 from a lower surface 191 of the optical disc 190, is formed in the boundary layer. In this state, if each blade of the plurality of blades 110 is installed as shown in FIG. 1B, the velocity gradient 150 of the boundary layer which is generated on the lower surface 191 of the optical disc 190 is removed while air flow passes through an incline of the blade 110. Thus, the air flow has a uniform velocity 160 toward the seating surface 101 of the disc tray 100 from the lower surface 191 of the optical disc 190. Accordingly, noise due to the velocity gradient 150 that is formed in the boundary layer is decreased.
However, in the conventional apparatus to decrease noise in the optical disc drive, the disc tray 100 is assumed to be a perfectly flat plate having openings. That is, the effect of the window 170, provided on the disc tray 100 so that the optical pickup (not shown) may access the recording surface of the optical disc 190, is excluded.
Vibration and noise are generated by friction between a high velocity rotating optical disc surface and air flow, and becomes severe as the velocity gradient and pressure gradient of air increase. From this point of view, the window 170 is a portion in which large variations in the velocity gradient and the pressure gradient of air flow appear.
FIG. 2 shows a vortex that is generated in a window of a conventional disc tray. As shown in FIG. 2, when the optical disc 190 rotates in a direction as shown by reference numeral 180, air flows in between a seating surface 201 and the optical disc 190 through a window 210, as shown by reference numeral 230. Then, a velocity gradient 220 of air gradually increases toward the seating surface 201 of the disc tray 200 from the lower surface 191 of the optical disc 190, and gradually increases toward an outside along the radial direction of the optical disc 190. As a result, a large vortex 240 is formed over the window 210 such that there is a great difference between pressures on right and left sides 250 and 260 of the window 210 and pressure in the window 210. The difference causes the vibration of the optical disc 190.
In addition, noise occurs at a boundary between the seating surface 201 and the window 210. Hence, in order to decrease noise and vibration in the optical disc drive, a vortex generated in the window and the pressure gradient of air should be removed or decreased.